Icing in a cold environment causes many problems, including glazing rotors and blades of wind turbines, breaking power lines, and stalling airfoil of aircrafts. Most of these problems are due to build-up of ice on surfaces. Such ice build-up may be removed by heating, by applying chemicals that reduce the melting point of ice, by applying a mechanical force (such as shock or vibration), or by occluding air to break the bonding between ice and the substrate surface. However, all of these methods have limitations and disadvantages. An alternative method to prevent ice build-up is to protect the surface with a coating that has an ultra-low ice adhesion strength (i.e., ice barely adheres to the coating), so that ice formed on such a coating can be released by the weight of ice alone when the substrate surface is slightly inclined from horizontal or by a very small shear force applied to the ice (e.g., by spinning of the blade of a wind turbine or by flowing of air over the surface).
Many approaches have been explored to make coatings for prevention of ice build-up, for example, by using coatings with a low surface free energy (such as silicone resins, fluorinated polymers, polyethylene, hydrophobic polyurethanes, epoxies, etc.), and by tuning the surface texture and roughness of the coating to reduce the contact area between ice and the substrate and/or to induce cracking of ice. In general, coatings made by following these approaches are able to significantly reduce the ice adhesion strength to substrates, sometimes by an order of magnitude or more, and consequently, ice may be released considerably easier from these coatings than from uncoated conventional substrates such glass, metals, and concrete. However, the ice adhesion strength on these coatings, even though significantly smaller than on uncoated substrates, is still too strong to satisfy the need of many industrial applications, and spontaneous ice release is still impossible in most circumstances. In quantitative terms, the shear stress that is required to release ice from these substrates (at about −20° C.) is in the order of 10-100 kPa, compared to the order of 100-1000 kPa for ice adhesion to uncoated metal and glass; however, the shear stress for ice release needs to be smaller than 10 kPa for spontaneous ice release in many applications. In some circumstances, ice adhesion strength is characterized by a cohesive strength in terms of adhesion energy per contact area, in which case it is generally believed that adhesion strength in the order of 0.1 J/m2 is required for spontaneous ice release. Heretofore, no viable technology has been able to produce coatings with such low ice adhesion strength.
Most recently, superhydrophobic surfaces have been used to prevent ice formation and to reduce ice adhesion on substrates. These surfaces show remarkable water repellency, characterized by a water contact angle of higher than 150°, which has been explained by the interplay between the surface chemical composition and the surface texture with a two-tier roughness in micrometer and nanometer scales, respectively, for each tier. Although some promising experimental results have been demonstrated which indicate that superhydrophobic surfaces may prevent ice formation and reduce ice adhesion strength in certain circumstances, it has been found that the superhydrophobicity of these surfaces is completely removed and ice adheres strongly to the substrates when condensation occurs before or with icing.
Thus, there remains a considerable need for ice release compositions for use as or in coatings, paints and the like for a wide range of surfaces and applications that provide ice adhesion strengths smaller than 10 kPa for spontaneous or easy ice release.